The present invention concerns the detection of fault conditions or failures in an internal combustion engine. In particular, the invention contemplates a system and method for detecting engine faults that are a product of engine valve and valve-related failures.
The typical internal combustion engine relies upon an arrangement of valves to control the intake and exhaust of gases to and from an engine cylinder. In a typical arrangement, the valves are spring-mounted within the engine block or head. The movement--i.e. the opening and closing--of the valves is typically controlled by a rocker assembly. The rocker assembly is driven by the engine crankshaft and utilizes an arrangement of cams to control the timing of the stroke of the valves in each cylinder.
Internal combustion engines include at least one valve per cylinder. In the case of a single valve cylinder, the valve is opened once for air intake, and a second time for exhausting combustion gases. In another type of engine, two such valves are provided, one for intake and one for exhaust.
Air is supplied to the engine cylinders by way of an arrangement of manifolds. One type of engine is shown in FIG. 1, utilizing eight cylinders in a standard V-arrangement. Thus, the engine 10 includes a left cylinder bank 11 and a right cylinder bank 12. In this instance, the engine 10 can be regarded as divided into four cylinder sections or quadrants, with each quadrant being supplied by a separate intake manifold. For example, the two upper left cylinders in the figure are supplied with air through the left front air intake manifold 15. In a similar fashion, the right front quadrant of the engine 10 is fed through the right front air intake manifold 16, the left rear quadrant through the left rear air intake manifold 17, and the right rear by the right rear air intake manifold 18.
As mentioned above, each cylinder is provided with an array of one or more valves. A typical valve assembly 30 is depicted in FIG. 2. The valve assembly 30 is mounted within the engine head 31. For an intake valve, the valve assembly is arranged between the air intake 32 and the engine cylinder chamber 33 to control the flow of air drawn from the intake and manifold into the cylinder.
The valve assembly includes a valve stem 35 that terminates in a valve head 36. The valve head 36 is configured to seal against a valve seat 37 disposed between the air intake 32 and the cylinder chamber 33. When it is operating properly, the valve head 36 is unseated from the valve seat 37 to introduce air into the cylinder chamber 33, and then subsequently sealed against the valve seat 37.
The engine head 31 supports a valve guide 39 through which the valve stem 35 reciprocates. An arrangement of springs, namely an outer spring 40 and an inner spring 41, provide an upward force to the valve stem 35. In this embodiment, a spring washer 42 is engaged at the end of the valve stem to trap the springs 40, 41 between the washer and the valve guide 39. The springs 40 and 41 are designed to provide an appropriate return force to pull the valve head 36 back into sealing engagement with the valve seat 37 at an appropriate time in the engine cycle.
The downward movement of the valve stem 35, and consequently the valve head 36, is governed by a rocker assembly 45. A tappet 44 at one end of the rocker assembly pushes down on the top of the valve stem 35 to free the valve head 36 from the valve seat 37. When the tappet 44 is retracted, the springs 40 and 41 operate to draw the valve head back into engagement with the seat 37.
As with any mechanical device, the valve assembly 30 is susceptible to failure in the harsh environment of the engine. Failures of the valve assembly range from minor to severe. Minor problems may start with leakage due to poor seating of the valve head 36 within the valve seat 37. This poor seating may be due to warping of the valve, the valve seat or the valve guide. As the amount of valve leakage increases, severe problems can result, including overheating of the valve and ultimately complete failure. Other failure modes of the valve assembly include burning and/or breakage of the valve stem or the valve seat. In addition, the valve springs may fail due to fatigue.
Failures of a valve assembly, such as a valve assembly 30, are difficult to detect. Undetected valve-related failures may progress rapidly and can quickly lead to major engine damage. Depending on the nature of the failure, severe damage to an engine can result in less than five minutes. In some cases, pistons, cylinder liners and cylinder heads, as well as fuel injector and connecting rods, can be irreparably damaged due to the effects of a failed valve assembly. Naturally, failures of this degree lead to significant engine downtime. In many applications, such as a mining operation an engine is expected to run 24 hours a day, seven days a week. In these applications, any downtime leads to additional consequential financial injury to the vehicle owner/operator.
Modern engines include an engine control system that continuously monitors several engine operating conditions, such as engine speed, oil pressure and temperature, coolant pressure and temperature, etc. For some engine problems, these monitored conditions provide a timely warning to the vehicle operator before the problems become more severe. However, in the case of valve-related failures, the normally monitored engine operating conditions do not provide adequate warning before severe and even catastrophic engine failures occur. There is therefore a need for a system and method that can accurately and timely detect a valve-related failure and notify the vehicle operator in sufficient time to avoid much more serious damage to the engine.